Future Hall of Fame quarterback Tom Brady follows a strict diet that he partially credits for his long and relatively injury-free NFL career. He and his family eat a predominantly plant-based diet loaded with vegetables and devoid of ultra-processed foods—diet choices that any nutrition expert can get behind. But there are a few quirks about his diet that raise a red flag. One in particular is the avoidance of nightshade vegetables due to the idea that they promote inflammation. This notion—that nightshades cause inflammation—is often reported by popular media outlets, or claimed by fad-diet gurus. Is there any evidence that nightshades cause inflammation? And what exactly is a nightshade vegetable?

The term nightshade refers to a family of plants with over 2,000 species. Some of these species are extremely toxic and have been used as poison for centuries. They’ve even been featured in popular culture. For example, Atropa belladonna, or “deadly nightshade,” likely inspired the poisonous “nightlock” berries in The Hunger Games. The poisonous and hallucinogenic plants Mandragora officinarum, or “mandrake” and Datura stramonium, or “devil’s snare,” were thought to be used by witches in medieval Europe. They were also used by modern-day fictional wizards and witches in the Harry Potter books.

Even tomatoes were referred to as “poison apples” in late 18^th century Europe after numerous reports of people falling ill and occasionally dying after frequent consumption. It turned out to be the lead-containing pewter plates that, when in contact with the acidic tomatoes, leached lead into the food causing lead poisoning. The accomplice role that tomatoes played was enough to raise and maintain suspicion years after the truly guilty party was identified.   

So yes, some nightshade plants are very toxic, and thus, should be avoided. Just like we should avoid eating off of lead plates. But what about edible nightshade species such as potatoes, tomatoes, eggplant, peppers, tomatillos, okra, sorrel, goji berries and gooseberries? Do these cause inflammation or undermine our health in any way?

To date, there are no human studies suggesting that nightshades cause or increase inflammation. This holds true for people with autoimmune diseases who are often looking to reduce inflammation. In fact, a couple of studies have found the exact opposite—that adding tomatoes or colorful potatoes to our diet may actually reduce inflammation. ₁₋₂

According to the research, the only negative effects of consuming nightshades are:

• Heartburn from eating spicy peppers
• Toxicity when consuming potatoes that have turned green (a sign that they are past due)
• All of the negative health effects associated with smoking tobacco (which is part of the nightshade family)

In other words, don’t smoke tobacco, avoid green/spoiled potatoes and avoid spicy peppers if they give you heartburn. But other than that, edible nightshades appear quite good for us with many offering unique benefits.

Here are some health benefits we can take advantage of by consuming edible nightshades:

• If you can handle the heat, eating peppers, which contain the spicy compound capsaicin, has been shown to slow cancer cell growth in a petri dish, and may improve blood vessel health and alleviate symptoms of irritable bowel syndrome. ₃₋₆
• For men, consuming more lycopene, the red pigment in tomatoes, appears to lower their risk of prostate cancer. ₇₋₉
• Goji berries and gooseberries are jam-packed with antioxidants that keep us healthy on a cellular level.
• Potatoes are a great source of potassium, which may help protect against stroke. Just be sure to consume them baked or boiled, and not fried or slathered with butter.
• Nicotine found in nightshade vegetables may help protect against Parkinson’s disease. Yes, you read that right. Some nightshade species contain nicotine, which may offer protection against Parkinson’s. Although tobacco is the most obvious source, other species contain far smaller amounts that will not lead to addiction. And in the one study, researchers found that nicotine consumption from foods like eggplant, tomatoes, potatoes, and especially peppers, was associated with lower rates of Parkinson’s disease. ₁₀ This may partially explain why populations eating a Mediterranean diet rich in these foods have low rates of neurodegenerative diseases, including Parkinson’s.

THE BOTTOM LINE

In summary, no, nightshade vegetables do not cause inflammation and, in general, are not detrimental to our health. In fact, the evidence suggests the contrary, that edible nightshades offer a variety of health benefits. Continue to include them in your diet as you please. And rest assured, none of the truly poisonous species will be found in your local grocery store.

References:

1. Jacob, K., Periago, M., Böhm, V., & Berruezo, G. (2008). Influence of lycopene and vitamin C from tomato juice on biomarkers of oxidative stress and inflammation. British Journal of Nutrition, 99(1), 137-146. doi:10.1017/S0007114507791894
2. Kaspar KL, Park JS, Brown CR, et al. Pigmented potato consumption alters oxidative stress and inflammatory damage in men. The Journal of Nutrition. 2011 Jan;141(1):108-111. DOI: 10.3945/jn.110.128074.
3. Chu-Sook Kim, Won-Hyung Park, Jun-Young Park, Ji-Hye Kang, Mi-Ock Kim, Teruo Kawada, Hoon Yoo, In-Seob Han, and Rina Yu.Journal of Medicinal Food.Sep 2004.267-273.http://doi.org/10.1089/jmf.2004.7.267
4. Jeong-Ki Min, Kyu-Yeon Han, Eok-Cheon Kim, Young-Myeong Kim, Sae-Won Lee, Ok-Hee Kim, Kyu-Won Kim, Yong Song Gho and Young-Guen Kwon Cancer Res January 15 2004 (64) (2) 644-651; DOI: 10.1158/0008-5472.CAN-03-3250
5. Chularojmontri L, Suwatronnakorn M, Wattanapitayakul SK. Influence of capsicum extract and capsaicin on endothelial health. Journal of the Medical Association of Thailand = Chotmaihet Thangphaet. 2010 Feb;93 Suppl 2:S92-101.
6. Bortolotti M, Porta S. Effect of red pepper on symptoms of irritable bowel syndrome: preliminary study. Dig Dis Sci. 2011;56(11):3288-3295. doi:10.1007/s10620-011-1740-9
7. Gann PH, Ma J, Giovannucci E, et al. Lower prostate cancer risk in men with elevated plasma lycopene levels: results of a prospective analysis. Cancer Res. 1999;59(6):1225-1230.
8. Giovannucci E, Ascherio A, Rimm EB, Stampfer MJ, Colditz GA, Willett WC. Intake of carotenoids and retinol in relation to risk of prostate cancer. J Natl Cancer Inst. 1995;87(23):1767-1776. doi:10.1093/jnci/87.23.1767
9. Lu QY, Hung JC, Heber D, et al. Inverse associations between plasma lycopene and other carotenoids and prostate cancer. Cancer Epidemiol Biomarkers Prev. 2001;10(7):749-756.
10. Nielsen SS, Franklin GM, Longstreth WT, Swanson PD, Checkoway H. Nicotine from edible Solanaceae and risk of Parkinson disease. Ann Neurol. 2013;74(3):472-477. doi:10.1002/ana.23884